means An expression of gratitude offered to someone who has helped, given, or done something for you.

from From Old English 'þanc,' which originally meant 'thought' — the same root that gives us 'think.' The leap from thought to gratitude makes a kind of quiet sense: to thank someone was to keep them in mind, to hold the favor in your thoughts. It's a cousin of German 'Dank' and Dutch 'dank,' all tracing back to a Proto-Germanic root tangled up with thinking and feeling. So every 'thanks' is, at its heart, an old promise: I'll remember this.